1. Field of the Invention
The present invention relates to a knocking discrimination apparatus for detecting a knocking taking place in an internal combustion engine and discriminating a degree of magnitude thereof, for instance, so as to insure a favourable performance of the engine by controlling an ignition timing in response to the state of knocking.
2. Description of the Prior Art
It is well known that, although the continuation of a state of strong knocking in an ordinary internal combustion engine has an injurious effect upon the durability and others of the engine, an optimum state of an output power and a performance of fuel consumption can be obtained by a state of slight knocking under a condition of comparatively low speed operation of the engine. So that, such a conventional equipment has been provided that the performances of output power and fuel consumption are improved by shifting the ignition timing with response to the detected state of knocking of the engine, so as to maintain the state of slight knocking based on the above close relation between the knocking and the ignition timing. Accordingly, it is required for this kind of equipment to develop an apparatus for discriminating the magnitude and the state of the knocking accurately.
As a conventional knocking discrimination apparatus of this kind, such an apparatus as shown in FIG. 1 is well known. In this apparatus, an output of a vibration or a knocking sensor 1 which is fitted on the internal combustion engine proper and a reference signal derived from a reference signal generator 2 are compared with each other in a comparator 3, so as to discriminate that a knocking, the former caused by which is larger than the latter, is necessary to be brought under the predetermined control.
However, the conventional knocking discrimination apparatus provided with the above mentioned simple configuration has such a defect that the discrimination of the knocking cannot be effected correctly, because the output of the knocking sensor is varied in response to the operating condition of the engine, and large noise components other than that of knocking are intermixed.
Accordingly, such apparatus as shown in FIGS. 2(a), (b) are employed in practice. In the apparatus shown in FIG. 2(a), a vibration sensor having a high resonant frequency in a range of 20-25 KHz and a flat sensing performance in a frequency range of about 0-10 KHz is used as the knocking sensor 1, an output signal thereof being applied to a comparator 3 through a bandpass filter 4 provided with a passband coinciding with a frequency range of the knocking and a half-wave rectifier 5. A part of the output signal passing through the halfwave rectifier 5 is averaged over a certain time duration by an averaging circuit 6, so as to form the aforesaid reference signal to be applied to the comparator 3 by adding or multiplying a predetermined number thereto. According to the above mentioned circuit configuration, even if the output level of the knocking sensor 1 is varied in response to the variation of operating condition of the engine, the reference signal to be compared therewith is varied also therewith, so that the correct discrimination of the knocking can be effected regardless of the operating condition of the engine.
In the apparatus shown in FIG. 2(b), an output signal of a knocking sensor 1 being similar to that shown in FIG. 2(a) is applied to a comparator 3 through a bandpass filter 4 similarly. On the other hand, a reference signal to be compared therewith is formed by driving a function generator 7 in response to the number of revolution of the engine which exerts an important effect upon the output level of the knocking sensor 1 particularly. Accordingly, the reference signal can be varied with response to the variation of the output signal of the knocking sensor 1 similarly as in the apparatus shown in FIG. 2(a), so as to realize the correct discrimination of the knocking.
The statuses of the above mentioned comparisons between the output signal of the knocking sensor and the reference signal are shown in FIGS. 3(a) and (b) respectively, the former relating to an operating condition of low speed and light load and the latter relating to another operating condition of high speed and heavy load.
However, in the above mentioned conventional apparatus, such a system that the level of the reference signal is varied in response to the variation of the output signal of the knocking sensor is adopted, so that it is feared that the reliability of the discrimination of the knocking is lower than that which can be obtained in such a case that the reference signal for the comparison is fixed to a certain specified level.